Align DU case augmentation with previous behavior in EraseUnions

docs/release-notes/.FSharp.Compiler.Service/8.0.300.md

@@ -11,6 +11,7 @@
 
 ### Changed
 
+* Autogenerated .Is* members for unions skipped for single-case unions. ([PR 16571](https://github.com/dotnet/fsharp/pull/16571))
 * `implicitCtorSynPats` in `SynTypeDefnSimpleRepr.General` is now `SynPat option` instead of `SynSimplePats option`. ([PR #16425](https://github.com/dotnet/fsharp/pull/16425))
 * `SyntaxVisitorBase<'T>.VisitSimplePats` now takes `SynPat` instead of `SynSimplePat list`. ([PR #16425](https://github.com/dotnet/fsharp/pull/16425))
 * Reduce allocations in compiler checking via `ValueOption` usage ([PR #16323](https://github.com/dotnet/fsharp/pull/16323))

src/Compiler/Checking/CheckDeclarations.fs

@@ -866,7 +866,8 @@ module AddAugmentationDeclarations =
 
     let ShouldAugmentUnion (g: TcGlobals) (tycon: Tycon) =
         g.langVersion.SupportsFeature LanguageFeature.UnionIsPropertiesVisible &&
-        HasDefaultAugmentationAttribute g (mkLocalTyconRef tycon)
+        HasDefaultAugmentationAttribute g (mkLocalTyconRef tycon) &&
+        tycon.UnionCasesArray.Length > 1
 
     let AddUnionAugmentationValues (cenv: cenv) (env: TcEnv) tycon =
         let tcref = mkLocalTyconRef tycon

src/Compiler/SyntaxTree/ParseHelpers.fs

@@ -1159,7 +1159,7 @@ let mkSynField
 
             let mType, mStart =
                 idOpt
-                |> Option.map _.idRange
+                |> Option.map (fun x -> x.idRange)
                 |> Option.orElseWith (fun _ -> vis |> Option.map (fun v -> v.Range))
                 |> Option.orElse isMutable
                 |> Option.orElseWith (fun _ -> leadingKeyword |> Option.map (fun k -> k.Range))

tests/FSharp.Compiler.ComponentTests/Language/DiscriminatedUnionTests.fs

@@ -17,6 +17,20 @@ if foo.IsBar then failwith "Should not be Bar"
         |> compileExeAndRun
         |> shouldSucceed
 
+    [<FSharp.Test.FactForNETCOREAPP>]
+    let ``Simple Is* discriminated union properties are not visible for a single case union`` () =
+        Fsx """
+type Foo = Bar of string
+let foo = Foo.Bar "hi"
+if not foo.IsBar then failwith "Should be Bar"
+
+        """
+        |> withLangVersionPreview
+        |> typecheck
+        |> shouldFail
+        |> withDiagnostics  [Error 39, Line 4, Col 12, Line 4, Col 17, "The type 'Foo' does not define the field, constructor or member 'IsBar'. Maybe you want one of the following:
+   Bar"]
+
     [<FSharp.Test.FactForNETCOREAPP>]
     let ``Simple Is* discriminated union property satisfies SRTP constraint`` () =
         Fsx """

tests/service/ExprTests.fs

@@ -3442,7 +3442,6 @@ let ``Test ProjectForWitnesses2`` useTransparentCompiler =
          "member Neg(p) = {x = Operators.op_UnaryNegation<Microsoft.FSharp.Core.int> (fun arg0_0 -> LanguagePrimitives.UnaryNegationDynamic<Microsoft.FSharp.Core.int,Microsoft.FSharp.Core.int> (arg0_0),p.x); y = Operators.op_UnaryNegation<Microsoft.FSharp.Core.int> (fun arg0_0 -> LanguagePrimitives.UnaryNegationDynamic<Microsoft.FSharp.Core.int,Microsoft.FSharp.Core.int> (arg0_0),p.y)} @ (7,34--7,56)";
          "member op_Addition(p1,p2) = {x = Operators.op_Addition<Microsoft.FSharp.Core.int,Microsoft.FSharp.Core.int,Microsoft.FSharp.Core.int> (fun arg0_0 -> fun arg1_0 -> LanguagePrimitives.AdditionDynamic<Microsoft.FSharp.Core.int,Microsoft.FSharp.Core.int,Microsoft.FSharp.Core.int> (arg0_0,arg1_0),p1.x,p2.x); y = Operators.op_Addition<Microsoft.FSharp.Core.int,Microsoft.FSharp.Core.int,Microsoft.FSharp.Core.int> (fun arg0_0 -> fun arg1_0 -> LanguagePrimitives.AdditionDynamic<Microsoft.FSharp.Core.int,Microsoft.FSharp.Core.int,Microsoft.FSharp.Core.int> (arg0_0,arg1_0),p1.y,p2.y)} @ (8,33--8,68)";
          "type MyNumber";
-         "member get_IsMyNumber(this) (unitArg) = (if this.IsMyNumber then True else False) @ (10,5--10,13)";
          "member get_Zero(unitVar0) = MyNumber(0) @ (12,25--12,35)";
          "member op_Addition(_arg1,_arg2) = let x: Microsoft.FSharp.Core.int = _arg1.Item in let y: Microsoft.FSharp.Core.int = _arg2.Item in MyNumber(Operators.op_Addition<Microsoft.FSharp.Core.int,Microsoft.FSharp.Core.int,Microsoft.FSharp.Core.int> (fun arg0_0 -> fun arg1_0 -> LanguagePrimitives.AdditionDynamic<Microsoft.FSharp.Core.int,Microsoft.FSharp.Core.int,Microsoft.FSharp.Core.int> (arg0_0,arg1_0),x,y)) @ (13,23--13,33)";
          "member DivideByInt(_arg3,i) = let x: Microsoft.FSharp.Core.int = _arg3.Item in MyNumber(Operators.op_Division<Microsoft.FSharp.Core.int,Microsoft.FSharp.Core.int,Microsoft.FSharp.Core.int> (fun arg0_0 -> fun arg1_0 -> LanguagePrimitives.DivisionDynamic<Microsoft.FSharp.Core.int,Microsoft.FSharp.Core.int,Microsoft.FSharp.Core.int> (arg0_0,arg1_0),x,i)) @ (15,31--15,41)";

tests/service/ProjectAnalysisTests.fs

@@ -714,11 +714,11 @@ let ``Test project2 all symbols in signature`` () =
              "DUWithNormalFields"; "member get_IsD"; "member get_IsDU1"; "member get_IsDU2";
              "property IsD"; "property IsDU1"; "property IsDU2"; "DU1"; "field Item1";
              "field Item2"; "DU2"; "field Item1"; "field Item2"; "D"; "field Item1";
-             "field Item2"; "DUWithNamedFields"; "member get_IsDU"; "property IsDU"; "DU";
+             "field Item2"; "DUWithNamedFields"; "DU";
              "field x"; "field y"; "GenericClass`1"; "generic parameter T"; "member .ctor";
              "member GenericMethod"; "generic parameter U"] |> List.sort
 
-    shouldEqual e r
+    shouldPairwiseEqual e r
 
 [<Test>]
 let ``Test project2 all uses of all signature symbols`` () =
@@ -736,12 +736,10 @@ let ``Test project2 all uses of all signature symbols`` () =
                ("generic parameter T",
                 [("file1", ((22, 23), (22, 25))); ("file1", ((22, 30), (22, 32)));
                  ("file1", ((22, 45), (22, 47))); ("file1", ((22, 50), (22, 52)))]);
-               ("member get_IsD", []);
-               ("member get_IsDU", []);
+               ("member get_IsD", []);             
                ("member get_IsDU1", []);
                ("member get_IsDU2", []);
-               ("property IsD", []);
-               ("property IsDU", []);
+               ("property IsD", []);            
                ("property IsDU1", []);
                ("property IsDU2", []);
                ("DUWithNormalFields", [("file1", ((3, 5), (3, 23)))]);